Field of the Invention
The invention is directed to the determination of the position of loads suspended from a carrying cable in hoists that are one-dimensionally or multi-dimensionally moved by corresponding actuating drives.
The stopping of a crane or of the load suspended from the crane over a set-down point normally causes an overshooting or swinging of the load. The time delay for the set-down event resulting therefrom leads to a considerable lengthening of the overall transport time of the load. Rocking or, respectively, swinging of the load, however, can be entirely or partially stabilized by movements of the crab or, respectively, of the crane or of the actuating drives executed correspondingly anti-phase. The constant position measurement of the load suspension means is necessary therefor, whereby a defined point, the load suspension point, is expediently considered. In the general case, the lateral position in the x-direction and y-direction of the coordinate system must be identified with a precision of below +/-1 cm proceeding from the crab plane. The measuring time connected therewith should not exceed a few milliseconds. Such measurements are usually implemented in non-contact fashion and leads to a position determination in space. These measurements, however, are disrupted by certain environmental conditions such as temperature, rain, snow, darkness or bright sunlight and the like.
Currently known methods for an average position action of the above type are implemented either by an opto-electronic acquisition of the load suspension point or via a swing angle measurement with mechanical or magnetic measuring means in the proximity of the cable suspension during operation of the crab. Given the latter method, however, cable undulations can considerably falsify the measured result. In the first-cited, opto-electronic method, the acquisition of the load suspension point is negatively influenced by the environmental conditions. Thus, the dependability of these methods is not always assured. Over and above this a two-dimensional position determination within a few milliseconds presents difficulties. Although optical reflectors or infrared light sources have been applied in the meantime for better recognition of the load suspension means for the opto-electronic method, these devices cannot eliminate the disadvantages of said method.